1. Field of the Invention
The invention generally relates to the field of biomedical testing. More particularly, the present invention relates to methods and apparatus for noninvasive tissue analyte determination.
2. Description of Related Art
Noninvasive Measurement of Glucose
Diabetes is a leading cause of death and disability worldwide and afflicts an estimated sixteen million Americans. Complications of diabetes include heart and kidney disease, blindness, nerve damage, and high blood pressure with the estimated total cost to United States economy alone exceeding $90 billion per year [Diabetes Statistics, Publication No. 98-3926, National Institutes of Health, Bethesda Md. (November 1997)]. Long-term clinical studies show that the onset of complications can be significantly reduced through proper control of blood glucose concentrations [The Diabetes Control and Complications Trial Research Group, The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus, N Eng J of Med, 329:977–86 (1993)]. A vital element of diabetes management is the self-monitoring of blood glucose levels by diabetics in the home environment. A significant disadvantage of current monitoring techniques is that of poor compliance due to the inconvenient and painful nature of drawing blood through the skin prior to analysis. Additionally, current glucose monitoring techniques involve the added cost of a disposable, one-use-only, test strip that is an additional and significant impediment to regular monitoring.
For the above reasons, new methods for self-monitoring of blood glucose levels are required to improve the prospects for more rigorous control of blood glucose in diabetic patients. A noninvasive glucose monitor addresses this problem and represents a significant and widely recognized advancement over the current state-of-the-art by eliminating the puncture wound used for drawing blood, the biohazard related to the invasive blood draw and the use of test strips.
Numerous approaches have been proposed for measuring blood glucose levels non-invasively, including:                Kromoscopy [see A. Helwig, M. Arnold, G. Small; Evaluation of Kromoscopy: Resolution of glucose and urea, Applied Optics, 39:4715–4720 (2000)];        Near-infrared Spectroscopy [see T. Blank, T. Ruchti, S. Malin and S. Monfre, The use of near-infrared diffuse reflectance for the non-invasive prediction of blood glucose, IEEE Lasers and electro-optics society newsletter, v.13:5 (October 1999); and R. Robinson, R. Eaton, D. Haaland, G. Keep, E. Thomas, B. Stalled, P. Robinson, Non-invasive glucose monitoring in diabetic patients: A preliminary evaluation, Clin Chem, 38:1618–22 (1992)];        Mid-Infrared Spectroscopy [see D. Klonoff, Mid-infrared Spectroscopy for Noninvasive Blood Glucose Monitoring, IEEE Lasers and electro-optics society newsletter, v.12:2 (April 1998)];        ATR (attenuated total reflectance);        Oscillating Thermal Gradient Spectrometry; [P. Zheng, C. Kramer, C. Barnes, J. Braig, B. Sterling, Noninvasive glucose determination by oscillating thermal gradient spectrometry, Diabetes Technology & Therapeutics, v.2:1, pp. 17–25 (2000)];        Far infra-red radiation spectroscopy;        Radio wave impedance;        Polarimetry;        Infrared and FT-IR Spectroscopy [see M. Shichiri, T. Uemura, K. Nishida, Non-invasive Fourier transformed infrared spectroscopy for the measurement of submucosal tissue glucose concentration, IEEE Lasers and Electro-optics Society Newsletter, v.12:2 (April 1998); and A. Bittner, H. Heise, T. Koschinsky, F. Gries, Evaluation of microdialysis and FT-IR ATR-spectroscopy for in-vivo blood glucose monitoring, Mikrochim. Acta [suppl.] 14:827–828 (1997)];        IR transmission [see M. Block, Noninvasive IR transmission measurement of analyte in the tympanic membrane, U.S. Pat. No. 6,002,953 (Dec. 14, 1999)];        Fluorescence (illuminescense) spectrometry;        Raman spectroscopy [see J. Chaiken, C. Peterson, Method for non-invasive measurement of an analyte, U.S. Pat. No. 6,377,828 (Apr. 23, 2002)];        Photoacoustic and pulse laser photoacoustic spectroscopy [see M. Chou, Method and apparatus for noninvasive measurement of blood glucose by photoacoustics, U.S. Pat. No. 6,049,728 (Apr. 11, 2000)];        Near-Infrared Scattering;        Emission spectroscopy;        Passive IR spectroscopy;        Bioelectric impedance or potentiometry, bioelectrical response spectroscopy; [see S. Siconolfi, Body Fluids Monitor, U.S. Pat. No. 6,125,297 (Sep. 26, 2000)]        Ultrasound;        Visible spectroscopy; and        Far infrared spectroscopy.        
Each method has associated advantages and disadvantages, but to date, no noninvasive technique for the self-monitoring of blood glucose has been certified by the United States Food and Drug Administration (USFDA). Consequently, an FDA approved product for consumer use based on any one of these technologies for the purpose of diabetes management through non-invasive glucose monitoring is not available. While the reasons impeding the progress of the various non-invasive technologies are diverse, a common and fundamental problem to these methods is the dynamic and diverse nature of the targeted tissue used to extract the information necessary to measure glucose [see O. Khalil, Spectroscopic and clinical aspects of non-invasive glucose measurements, Clin Chem, 45:165–77(1999); and S. Malin, T. Ruchti, An intelligent system for noninvasive blood analyte prediction, U.S. Pat. No. 6,280,381 (Aug. 28, 2001); and T. Blank, T. Ruchti, S. Malin and S. Monfre, The use of near-infrared diffuse reflectance for the non-invasive prediction of blood glucose, IEEE Lasers and Electro-Optics Society Newsletter, v.13:5, (October 1999); and G. Cote, Noninvasive optical glucose sensing—an overview, J. Clin. Eng., pp. 253–259 (July/August 1997); and R. Waynant, V. Chenault, Overview of non-invasive fluid glucose measurement using optical techniques to maintain glucose control in diabetes mellitus, IEEE Lasers and electro-optics society newsletter, v.12:2 (April 1998); and H. Heise, Near-infrared Spectrometry for in vivo glucose sensing, in Biosensors in the Body: Continuous In Vivo Monitoring, D. Fraser, ed., John Wiley & Sons (1997)]. While each targets a modification to a particular excitation or probing signal by the concentration or presence of glucose, the interfering substances, constituents, and dynamic properties of tissue together with the trace level of glucose have rendered the goal of creating a reliable device elusive. Thus, it would be a significant technical advance to provide a method foe measuring glucose non-invasively that overcomes these pervasive problems.